Galaxies are found in clusters and sometimes the clusters contain red and dead member that have stopped forming stars.

The latest discovery has found that comatose galaxies can sometimes come back to life.

If the clusters of galaxies merge, a huge shock wave can drive the birth of a new generation of stars, and the sleeping galaxies get a new lease of life.

The research is led by Andra Store of Leiden Observatory and David Sobral of Leiden and University of Lisbon.

Galaxy clusters are where thousands of galaxies are packed together. Over billions of years, they build up structure in the universe, by merging with the adjacent clusters.

When the clusters collide to merge there is huge release of energy, the resulting shock travels through the cluster.

Previously it was unknown that the collision will affect galaxies in the clusters.

Researchers have observed the merging cluster CIZA J2242.8+5301 which is nicknamed the Sausage, and located 2.3  billion light years away in the direction o the constellation of Lacerta in the northern hemisphere of the sky.

To observe the merging of galaxies they have used William Herschel and Isaac Newton telescope on La Palma, the Subara, Keck telescope and CFHT telescopes on Hawaii.

They found that the galaxies in the cluster are transformed by the shock wave produced after the collision, which led to a new wave of star formation.

Stroe said, “We assumed that the galaxies would be on the sidelines for this act, but it turns out they have a leading role, the comatose galaxies in the Sausage cluster are coming back to life, with stars forming at a tremendous rate. When we first saw this in the data, we simply couldn’t believe what it was telling us.”

Stroe said that the new findings implied that merging of galaxy cluster is having impact on star formation. It is like stirring teaspoon in a mug of coffee, the shocks leads to turbulence in the galactic gas, this triggers an avalanche like collapse leading to the formation of very dense, cold gas clouds, which are vital for the formation of new stars.

Store added, “But star formation at this rate leads to a lot of massive, short-lived stars coming into being, which explode as supernovae a few million years later, the explosions drive huge amounts of gas out of the galaxies and with most of the rest consumed in star formation, the galaxies soon run out of fuel. If you wait long enough, the cluster mergers make the galaxies even more red and dead – they slip back into a coma and have little prospect of a second resurrection.”

Every cluster has experienced a series of mergers during its lifetime, so they should pass through a period of vigorous production of stars.

The shock will however only lead to a brief increase in star formation.

Astronomers are lucky to catch a cluster at a time of its evolution when the galaxies are still being lit up by the shock.

Now the astronomers need to find out if the Sausage cluster is unique and these bursts of star formation need very particular condition.

Astronomers believe that if they study much bigger sample of galaxies, they could find out exactly how they happen.